Fluid control valves and fluid flow systems are used throughout an automobile to control the flow of fluids. Examples of fluid flow systems include (a) air and exhaust gas recirculation (EGR) flow to combustion chambers or cylinders of an internal combustion engine, (b) water flow to control the cooling of an internal combustion engine, and (c) warm/cool air flow to moderate the temperature within the passenger compartment of a vehicle. These fluid flows are typically controlled by fluid control valves, especially solenoid operated valves.
It is now customary to utilize exhaust gas recirculation in the fuel management system of automotive internal combustion engines to reduce the amount of pollutants in the exhaust gas and to improve fuel economy. This is accomplished by capturing a portion of the exhaust gas and combining the captured exhaust gas with an air/fuel charge for the internal combustion engine. If the balance between the air, fuel and exhaust gas is such that an ideal stoichiometric mixture is achieved, then maximum power is produced while utilizing a minimum amount of fuel and creating a minimum amount of pollutants.
More specifically, incorporating exhaust gas into fuel and air being burned in combustion chambers is helpful for several reasons. First, pollutants, particularly nitrous oxides (NOx), are more susceptible to being produced when temperatures in combustion chambers are high. Exhaust gas has a higher specific heat than air and therefore the presence of exhaust gas in place of air assists in lowering temperatures in combustion chambers.
When less than full power from an engine is needed, the combustion chambers do not need a full compliment of air since a reduced amount of fuel is typically supplied to them. Accordingly, exhaust gas replaces a portion of the air such that the lesser amounts of fuel and air are again stoichiometrically balanced. With less air and fuel being burned, the amount of heat produced will be less, again keeping the temperature in the combustion chambers at a lower level and the amount of pollutants produced down.
Further, adding exhaust gas to intake air reduces the amount of work an engine must perform. The exhaust gas is generally at a positive pressure relative to the intake air. Therefore, the addition of this exhaust gas to intake air reduces the amount of vacuum which must be created by pistons to draw gases into the cylinders.
Care must be taken, however, not to provide an overabundance of exhaust air into the fuel/air/exhaust gas mixture. If too much exhaust gas is introduced, the engine can run roughly. Accordingly, the fuel/air/exhaust gas mixture introduced into the combustion chambers are typically controlled to insure that there is an overabundance of fuel and air at the expense of not supplying an optimal amount of exhaust gas. Looking to FIG. 1, curves 16A-D represent percentage maximum engine torque versus engine RPM for a variety of percentage throttle open positions. Encircled area 17 represents the theoretical portion of the graph in which exhaust gas should be added to intake air to achieve optimal gas mileage and reduced pollutants. Encircled area 18 shows a much reduced portion of encircled area 17 in which conventional engines are conservatively operated. Area 19, as discussed in more detail below, illustrates the general area of performance of the present invention. Thus, internal combustion engines today are not operated as efficiently as possible. This is in large part due to the present inability of solenoid valve mechanisms to precisely control the introduction of exhaust gas into an ambient air stream which is then directed to one or more combustion chambers for burning with fuel.
An exhaust gas recirculation valve of a poppet type is often used to provide some control of the amount of exhaust gas that is captured and returned to the internal combustion engine for reburning. In one known system, a mechanically actuated poppet valve has been used in which an electrical control signal controls a vacuum motor which, in turn, actuates a poppet valve member. However, the response of the vacuum motor-actuated poppet valve member is often too slow to precisely control the input of exhaust gas into intake air even when it is controlled by an electronic signal.
Some EGR systems utilize solenoid actuated poppet valve members to provide a quicker response. See for instance, U.S. Pat. Nos. 4,805,582, 4,961,413 and 5,094,218. However, as demonstrated by these patents, the pressure of the exhaust gas in known solenoid actuated EGR valves supplies forces tending to open the poppet valves members which are held in the closed position by spring mechanisms. This is a drawback because the arrangement requires the use of heavy springs to insure that the poppet valve members do not lift from their valve seats when the pressure of the exhaust gas is high, such as during engine backfire or under other engine load conditions.
Furthermore, since the solenoid activated EGR valve systems must overcome the heavy closing spring forces to open poppet valve members, relatively larger solenoids are required, which result in increased size and weight penalties for the systems. These penalties are important factors, particularly in automotive applications where weight affects fuel economy to such an extent that there are continuous and unrelenting ongoing efforts today to reduce weight.
Moreover, because springs, poppet valve members, and armatures in known systems are large and heavy, significant amounts of current must be supplied to the solenoids to overcome the large spring forces and open the poppet valve members. This, in turn, increases the load on the electrical system of the vehicle.
Finally, known EGR valves employing solenoids are often difficult to control. First, because of the relatively heavy or massive components used in constructing the EGR valves, the response time for armature and poppet valve member control can be slow. Also, vibration due to engine operation and vehicle bounce due to road surface irregularities can cause a massive armature to move independently of the remainder of the EGR valve mounted on a vehicle.
Second, current technology is not well suited to precisely identify the position of a poppet valve member relative to a valve seat. In this regard, the position of the poppet valve member determines the quantity of fluid flow through the EGR valve and is therefore significant. Potentiometer based sensors include a metallic conductor affixed to the housing and at lease one wiper operatively connected to a poppet valve member and/or an armature. The wiper slides relative to non-moving metallic conductors within the EGR valve to determine poppet valve member position. These potentiometer based sensors are susceptible to vehicle vibrations and continuous wear due to cycling of the components. Valves having potentiometer based sensors must be mechanically calibrated and are therefore difficult and time-consuming to calibrate during assembly. Further, their accuracy often significantly deteriorates over the operating life of an EGR valve.
Another problem with current solenoid actuated EGR valves is that they may allow air and exhaust gas to leak along the stems of poppet valve members and into and out of the EGR valves. This leakage detracts from the ability to carefully meter and balance the intakes of ambient air and exhaust gas through the EGR valves.
EGR systems typically contain conduits and orifices of a sufficient size to accommodate large amounts of exhaust gas flow. Looking to FIGS. 2A and 2B, exhaust gas is supplied at a positive pressure P.sub.P relative to atmosphere, when expelled during an exhaust stroke from combustion chamber C and into an exhaust manifold. Intake manifolds generally are at a relative negative pressure, P.sub.N, because an air/exhaust gas mixture is drawn into the combustion chambers C during intake strokes of pistons P, as shown in FIG. 2B. Accordingly, the flow of exhaust gas from the exhaust manifold, through an EGR valve V and into the intake manifold, is partially limited by the pressure drop between the manifolds. Therefore, the sizes of the conduits and orifices in the system must be sufficient to provide a desired maximum exhaust gas flow due to the available pressure drop in the exhaust and intake manifolds.
Internal combustion engines are also susceptible to clogging due to accumulation of contaminants and moisture carried by exhaust gases. Exhaust gases often contain heavy particles which can fall or settle out of suspension if fluid flow is too slow, or if the flow passes through a sharp bend. As a result, it is common for contaminants to build up in EGR valves or for heavy particles to accumulate within the intake manifold near the exhaust gas inlet and drop into the first available combustion chamber. Therefore, it is advantageous to mix exhaust gas and ambient air as homogeneously as possible to maintain the heavy particles in fluid suspension prior to entry into the combustion chambers.
Moreover, solenoid actuated EGR valves can fail if they overheat. Insulation on wires and coils of a solenoid can deteriorate if the temperatures in an EGR valve are too high. Therefore, care in design must be taken to insure that EGR valves are not subjected to excessively high temperatures.
Another problem encountered with EGR valves is that they are mounted on a wide variety of engines. Hence, different EGR valve configurations must be made for each different type of engine. This leads to a large amount of design work and a need to secure and keep available a significant inventory of EGR valves with different engine mounts.
Several of the problems with known EGR valves are also present with respect to known valve mechanisms for controlling water flow to cool engines. Solenoid activated valve mechanisms for these systems often are relatively large and massive due to the heavy biasing members and forces necessary to keep the valves closed. These valve mechanisms add undesirable weight to the vehicles, unnecessarily increasing the load on the electrical systems of the vehicles, and are difficult to control with accuracy and precision. The position of a moveable poppet valve member and thus the amount of valve opening and fluid flow is also difficult to control and measure, and can vary over the life of the valve mechanism. These problems may also exist with other vehicle and non-vehicle solenoid controlled valve applications involving fluid flow.